I sweated to get 42 mpg in the Chevrolet Cruze diesel, then pushed harder to wring 47 mpg.

In my first couple days of driving, the onboard computer indicated 35 to 36.3 mpg in combined city and highway driving. That beats the EPA combined rating of 33 mpg. But getting to the EPA’s 46 mpg highway rating would take finesse and patience.

It is a sturdy powertrain of a 151-horsepower, turbocharged, direct-injection 2.0-liter four-cylinder and six-speed automatic transmission.

On Day 3, I made a highway run of 204 miles and reached 42 mpg, but it wasn’t easy. I used cruise control set between 63 and 65 mph, depending on terrain. I watched the trip meter and was encouraged by every hard won tenth of a mile gained for average mpg. And I was frustrated at how easily the tenths went away on hills or with strong acceleration.

I wasn’t hyper-miling, but I did draft the occasional RV or big rig. And I watched traffic ahead to avoid erratic changes in speed, steering or braking.

I drove with the AC off as much as possible, but in the warm afternoon the windows fogged, I sweated and my shirt stuck to the leather seatback. I couldn’t detect any mpg benefit, so I switched on the AC.

Driving at or just below the speed limit – in the slower two lanes – allowed traffic to flow around me. But it was like dieting and watching others gulping what I could only nibble.

The Cruze is a comfortable long-range rover but some will like more lower back support to the front seats. The ride is steady and controlled with little noise sensitivity to changes in road surfaces. Standard features include 10 air bags, remote locking, leather-trimmed upholstery, six-way power driver seat (and six-way manual passenger seat), alloy wheels and extra soundproofing.

Even with a strong 264 foot-pounds of torque 2,600 rpm, performance is tuned to maximize mileage. The engine – clacking out a snory, snoozy sound – is good at cruising but not swift at grabbing gears for passing power.

42 mpg compares to the VW Jetta diesel, so the next day I went on a different Interstate run. Determined to hit 46 or bust, it took another 158.4 miles to hit my number. And I eventually coaxed 47 mpg from the run.

To do the math as advertised, the Cruze’s 15.6-gallon tank could return 717 miles of range. But in my test, with just over 525 miles on the odometer, the fuel gauge indicated about an eighth of a tank remained. I’d usually start looking for a filling station at the point, but the car computer claimed there were still 110 miles till empty.

But diesel has issues. The fuel is pricey, typically as much or more than a gallon of premium fuel. And the engine choice is more expensive than for a gasoline four-cylinder and comparable to a gasoline-electric hybrid. The cost benefit is in the driving range – the distance between fill-ups. A driver racking up 125 miles a day – and four to five hours a day behind the wheel – isn’t excited to make yet another fuel stop before or after work to be ready for the next day of driving.